The purpose of this study is to demonstrate the feasibility of methylphenidate (MPD) as effective and safe in the outpatient treatment of cocaine-dependent patients with a comorbid DSM-IV diagnosis of Attention Deficit Hyperactivity Disorder (ADHD), to demonstrate the ability of each site to participate in a subsequent anticipated controlled trial of MPD (recruitment and execution), and to gather preliminary data on the ability of sweat patches to detect episodes of cocaine use.